Pancreatic cancer is the fifth leading cause of death in the U.S. with a 5-year survival rate of less than 5%. Although radiotherapy and chemotherapy are the recommended treatments and have enjoyed some success, no current treatment effects 2-year survival for patients with locally advanced and metastatic disease (Lawrence, Semin. Oncol., 22:68-71, 1995).
A difficulty that is commonly encountered when treating patients that have pancreatic as well as other cancers with cytotoxic small molecule drugs is that the cytotoxin causes toxicity to normal tissues as well as cancerous tissues. One approach to obtain higher specificity for the cancer tissue is the use of antibodies that can target specific antigens expressed in cancer cells that are not expressed or are expressed at a lower level on normal cells. These target antigens can be exploited using antibodies to specifically kill antigen-bearing tumor cells by a variety of mechanisms including inhibiting the biological activity of the antigen, eliciting an immune effector activity by complement dependent cytotoxicity (CDC) and/or antibody dependent cellular cytotoxicity (ADCC), or by delivering immuno- or radio-conjugates that, when delivered to the antigen-bearing cell, specifically kill the target cell. Finding antibodies that can specifically bind to and effectively kill antigen-bearing tumor cells has proven difficult for many cancers. This has been due in part to the inability to obtain robust tumor lysis due to either a lack of immune effector function or of efficient internalization of antibodies carrying immunotoxins. Due to the expression profile for mesothelin in pathologic tissue, there is an opportunity to obtain tumor-specific targeting for several cancer types including but not limited to pancreatic, ovarian, and lung cancer and mesothelioma.
Mesothelin is a glycosylphosphatidylinositol (GPI)-linked glycoprotein synthesized as a 69 kDa precursor and proteolytically processed into a 30 kDa NH2-terminal secreted form and a 40 kDa membrane-bound form (Yamaguchi, et al. (1994) J. Biol. Chem. 269:805-808). Mesothelin is highly expressed on the surface of pancreatic cancers, ovarian cancers, mesotheliomas, lung cancers, and some other cancers. Its expression is limited on normal tissues, making it a potential target for cancer therapy. (Cao, et al., Mod. Pathol. 14:2005; Hassan, et al., Clin. Cancer Res. 2004 Jun. 15; 10(12 Pt 1):3937-42).
Administration of antibodies against mesothelin has been proposed as a strategy for treatment of mesothelioma as well as lung, ovarian, and pancreatic cancer. Full-length antibodies against mesothelin that can elicit a robust immune-effector activity and internalize for delivery of toxic conjugates, however, have not been previously developed.
In 1992, Chang et al. described monoclonal antibodies that recognized antigens on human ovarian carcinoma cells (Chang, et al., Am. J. Surg. Pathol. 1992 16:259-68). This antibody, called K1, was chemically conjugated to a truncated form of Pseudomonas exotoxin and found to bind mesothelin-positive cells and cancer cells. However, it was not useful as an immunotoxin conjugate due to its poor internalization ability. U.S. Pat. No. 6,083,502 describes mesothelin and uses for targeting and diagnosing mesothelin-positive cells using antibody K1.
Subsequent single chain antibodies were produced that bound with high-affinity and had potent antitumor activity on mesothelin-positive tumors as a conjugate. One such single chain antibody is SS1(scFv)-PE38 which has a high binding affinity (Kd of 0.7 nM) to mesothelin. This single chain antibody is a stabilized form of the Fv in which a disulfide bond connects the light and heavy chain domains of the Fv. SS1(scFv)-PE38 has been shown to have activity in killing tumor cells by internalization of the single chain antibody-immunotoxin complex (Hassan, et al., Clin. Cancer Res., 8: 3520-6, 2002; Hassan, et al., Proc. Am. Soc. Clin. Oncol., 21: 29a, 2002). Other groups have also developed antibodies that can bind to mesothelin and found overexpression of this antigen to be associated with various cancers (Scholler, et al., Proc. Natl. Acad. Sci. U.S.A. 1999 Sep. 28; 96(20):11531-6; Ordonez, Am. J. Surg. Pathol. 27:1418-28, 2003).
U.S. Pat. No. 6,809,184 describes a single chain high affinity antibody that binds to mesothelin at a different epitope than the K1 antibody. This antibody fragment was found to internalize in mesothelin-positive cells as a single chain fragment linked to an immunotoxin. The antibody was named SS1.
Attempts to develop immunoconjugated antibodies that can specifically target mesothelin have been performed with little success due to poor internalization and/or affinity (Hassan, et al., J Immunother. 2000 Jul.-Aug.; 23(4):473-9). This lack of internalization could be due to low affinity or poor internalization due to antibody composition and/or epitope binding. In addition, generation of the monoclonal antibody (mAb) K1 as an immunoconjugate was attempted because the unconjugated form was not cytotoxic itself (Hassan, et al., Clin. Cancer Res., 10:3937-3942, 2004).
Provided herein are in-out antibodies that can internalize in mesothelin-positive cells and elicit a cytotoxic effect via immune effector activity. Also provided are antibody therapies for cancer, in particular for mesothelin-positive cancers, for example, pancreatic, ovarian, mesothelioma, and lung cancers, using antibodies that elicit a robust immune effector activity yet retain the ability to internalize and facilitate the delivery of toxins to mesothelin-positive cells.